Pharmaceuticals intended for oral administration are typically provided in solid form as tablets, capsules, pills, lozenges, or granules. Tablets are swallowed whole, chewed in the mouth, or dissolved sublingually. Soft tablets that either are chewed or dissolve in the mouth are often employed in the administration of pharmaceuticals where it is impractical to provide a tablet for swallowing whole. With chewable tablets, the act of chewing helps to break up the tablet particles as the tablet disintegrates and may increase the rate of absorption by the digestive tract. Soft tablets are also advantageous where it is desirable to make an active ingredient available topically in the mouth or throat for both local effects or systemic absorption. Soft tablets are also utilized to improve drug administration in pediatric and geriatric patients. Soft tablets designed to disintegrate in the mouth prior to swallowing are particularly useful for improving compliance of pediatric patients.
Generally, soft tablets are made by direct compaction of a mixture of tabulating compounds including an active ingredient, flavoring, binders, etc. The mixture is fed into a die cavity of a tablet press and a tablet is formed by applying pressure. Hardness of the resulting tablet is a direct function of the compaction pressure employed and the compatibility of the ingredients in the formulation. A softer tablet, having an easier bite-through, may be prepared by employing reduced compaction pressures. The resulting tablet is softer, but also more fragile, brittle, and easily chipped.
Soft tablets designed to disintegrate in the mouth without chewing are disclosed by Cousin et al., in U.S. Pat. No. 5,464,632, and Wehling et al., in U.S. Pat. Nos. 5,223,264 and 5,178,878. While these soft tablets for oral administration advantageously disintegrate completely in the mouth prior to swallowing, they have the disadvantage of being highly friable, requiring costly specialized handling and packaging in order to prevent breakage.
It is known to apply outer coatings to a chewable tablet in order to protect the soft core. Typically, such outer coatings contain cellulose derivatives as major ingredients, which have relatively high melting points, i.e., greater than 135.degree. C. For example, PCT Application No. WO 93/13758 discloses the application of a thin layer of coating material such as a disaccharide, polysaccharide, or cellulose derivative onto a compressed tablet. U.S. Pat. No. 4,828,845 relates to the coating of a comestible with a coating solution comprising xylitol, a film-forming agent such as methyl cellulose, a binder, optionally a filler, and optionally a plasticizer such as polyethylene glycol, the balance of the solution being water. The plasticizer makes up only about 3 to 7 weight percent of the coating solution disclosed in the '845 patent. U.S. Pat. No. 4,327,076 discloses a compressed, soft, chewable tablet containing an antacid or other active ingredient that may be coated with a sealant or a spray coat of chocolate.
It has now been discovered that a soft tablet having a hardness of up to about 15 kp/cm.sup.2 may be coated with a molten composition comprising at least 50 weight percent of a thermoplastic material having a melting point of less than about 120.degree. C. The molten composition is solidified into a protective coating, and the coated tablet may, if desired, be further coated with one or more outer coatings made of conventional coating materials, such as saccharides, cellulose derivatives, and the like. Application of the protective coating according to the invention stabilizes the friability of the tablet. It also provides a water-resistant barrier for the tablet core. This is especially advantageous when its is desired to use conventional outer coatings on the tablet, which can erode the tablet core. By application of such outer coatings over the protective coating, the integrity of the tablet core is preserved.